Wlork is underway to synthesize prostaglandin derivatives with substituents in selected positions. Also, a specific synthesis leading to the D prostaglandins is underway. 13CNMR studies are being continued in the direction of preparing prostaglandins in which portions of the carbon skeleton are enriched with up to 90 percent C13. Biochemical procedures are being employed for the ssnthesis of both the polyunsaturated fatty acid precursors and of the prostaglandins themselves. These C13 enriched prostaglandins will be used for T1 measurements to ascertain specific binding areas when combined as substrates with the placental prostaglandin 15-dehydrogenase enzyme.